The present invention is described below with respect to an electro-optic liquid crystal shutter. It will be appreciated, though, that features of the invention may be utilized with shutters formed of materials other than liquid crystal and also may be utilized with devices other than shutters. A shutter, as is used herein, refers to a device for controlling intensity of electromagnetic energy or electromagnetic radiation that is being transmitted through the shutter. In the preferred embodiment described in detail below, such electromagnetic energy is in the form of light and more preferably is in the form of light (i.e., electromagnetic energy) that is in the visible spectrum as well as in the various infrared spectra and ultraviolet spectra, all collectively referred to as light below. Such control may be by way of graduated or analog control or intensity of transmitted light preferably without detrimentally affecting the image characteristics of such light. Such control also may be digital, i.e., on, off, and specific intermediate levels of transmission or intensity, etc.
A problem associated with existing electro-optic light shutters used as part of protective eye wear such as goggles, welding helmets, or the like, is that the driver circuit for driving the shutter can occupy a relatively large amount of space. As a result, the light shutter and driver circuit may be too large to fit in the lens aperture of the protective eye wear. For example, welding helmets usually are manufactured with a standard sized lens aperture. A welder can insert a variety of standard sized protective cover lenses and/or filters such as a shade filter or ultraviolet filter in the lens aperture as may be desired for eye protection under a particular condition, e.g., depending on the type of welding materials being welded, brightness of ambient light, etc. The lens aperture is standard sized so that the welder can select and insert a desired type of lens or filter based on the particular type of welding application. The lenses and filters are commercially available in the same standard sizes so the welder can change easily amongst the different types of lenses or filters.
An exemplary welding helmet having a standard size lens aperture (approx. 2 inches by 4.25 inches) is sold by Sellstrom as Model No. 295 11. An exemplary standard size lens is a "100% Cast Resin Welders Plastic Cover Lens" available from Wesco in Redwood City, Calif. U.S.A. Such a lens is manufactured, for example, under such standards as Federal Spec. GGG-H-211C and ANSI Std. Z87. Also, it will be appreciated that protective cover lenses, lenses and filters, as referred to herein, are referred to collectively as both lenses and cover lenses and are intended to be equivalent at least in the context of the invention.
Conventional electro-optic shutters are typically too large to be inserted into a standard size lens aperture. As a result, the standard size lens aperture in the welding helmet must be enlarged and the standard size lenses no longer fit in the aperture. Alternatively, the driver circuit for the shutter must be positioned in the helmet somewhere other than the lens aperture. This requires that the helmet be custom designed or modified to accommodate the driver circuit, resulting in additional expense and/or lost time.
Furthermore, a cover lens is useful for protecting the light shutter in addition to the eyes of the user. For example, the cover lens protects the light shutter from damage or dirt due to contact with fingers, etc. Also, sputtering, splash, spray, flying particles, etc., which may occur during welding, can damage the light shutter. Typically, therefore, a cover lens is included in the welding helmet lens aperture in front of the light shutter to protect the light shutter from damage due to such sputtering, etc.
In the event the cover lens itself becomes damaged, however, it is necessary to replace the cover lens. Therefore, again it is highly desirable that the welder be able to replace an existing cover lens with a standard size cover lens. If the light shutter requires a non-standard size cover lens, this may result in additional expense associated with nonstandard sized parts. Alternatively, production time can be lost and/or undesirable costs incurred as a result of having to modifying a standard size cover lens to tit the nonstandard sized shutter/aperture.
Still another drawback associated with conventional light shutters used as part of welding helmets or other protective eye gear is that the switching mechanism for turning the light shutter on and off is difficult to access and/or requires modification of the helmet and other standard size parts. For example, a conventional light shutter for a welding helmet includes an on/off switch on the light shutter frame assembly on the inside of the helmet. This requires that the welder take off the helmet in order to turn the shutter on and off. Obviously, this can be very inconvenient to the welder. Furthermore, some of such light shutters require a non-standard size cover lens so as to provide access to the on/off switch from the inside of the helmet.
In view of the aforementioned shortcomings associated with existing light shutters, there is a need for a light shutter including a drive circuit which can be inserted in a standard sized aperture of a welding helmet or the like. There is a need for such a light shutter which can be used with standard size cover plates to protect the light shutter and the eyes of a user from being damaged. Further, there is a need for such a light shutter with a switching mechanism for powering on and off the light shutter which can be easily activated. In particular, there is a need for a switching mechanism which does not require customization of the standard components associated with a welding helmet or the like, e.g., the helmet assembly or cover plates.
As will be appreciated based on the following detailed description, an exemplary liquid crystal shutter with which the invention may be utilized is disclosed in U.S. Pat. Nos. 4,385,806, 4,540,243, 4,582,396 and Re. 32,521. An example of such shutter includes a pair of linear (plane) polarizers, one being used as an input polarizer and the other as an output analyzer, and a variable liquid crystal optical retarder between the two polarizers. By changing the electric field applied to liquid crystal in the retarder, the plane of polarization (or relationships of the axes of elliptically polarized light) of the light transmitted through the retarder can be changed; and the intensity of light transmitted through the analyzer will be a function of the polarization direction (characteristics) of the light transmitted through the retarder.
A shutter system which may employ .such an exemplary liquid crystal shutter is disclosed in copending, commonly owned U.S. Pat. application Ser. No. 07/653,661 filed Feb. 8, 1991, for "Eye Protection System For Welding Helmets And The Like".
An exemplary driver circuit with which the present invention can be utilized is described in commonly assigned, co-pending U.S. Pat. application Ser. No. 07/674,850 filed Mar. 25, 1991, for "Liquid Crystal Lens Driver Electronics for Eye Protection and High Speed Shuttenng", and U.S. Pat. application Ser. No. 07/814,372 filed Dec. 26, 1991, for "Welding Arc Light Detector for Use with Electronic Eye Protection and High Speed Shuttering." The disclosures of the above patents and patent application are incorporated herein in their entireties by this express reference thereto.